Characterization of serum dipeptidyl peptidase IV activity in three diverse species of West African crocodilians

Serum dipeptidyl peptidase IV (DPPIV) activity was characterized in three divergent and sympatric species of West African crocodiles. The serum of the Nile crocodile (Crocodylus niloticus) exhibited higher DPPIV activity than that of the African dwarf crocodile (Osteolaemus tetraspis) and the slender-snouted crocodile (Mecistops cataphractus). Kinetic analyses showed that the rate of product formation was higher in serum of C. niloticus with respect to time, and it was confirmed by double reciprocal plot analysis that the V_max for serum of C. niloticus was higher than the other two species. However, the Michaelis constants were very similar for all three species, indicating that the C. niloticus DPPIV enzyme may be a more efficient catalyst. Thermal activity profiles demonstrated that the serum DPPIV activities of all three species increased substantially with temperature. Although activity of C. niloticus was higher than that of O. tetraspis and M. cataphractus at all temperatures investigated, linear increases of activity with temperature were noted for all three species. The results from this study show that three diverse species of West African crocodilians express soluble serum DPPIV.